Olive stones

Olive stones are a product of separation of the olive cake. Usually this is done by  centrifugation or by putting olive cake into the water. In both cases  olive stones are separated from the olive meat, olive skins and are used as a separate product.

If the centrifugation is used so called  “dark” olive stones are received as it is more difficult to make a separation by centrifuges and some olive skins and olive meat will be present. Ash content of olive stones  in these  cases  is on the level of 3-4%,anyhow over 2%. If the underwater method with later  drying process  is used so called “pale” olive stones can be produced. Quantity of produced olive stones  is significantly less than the olive cake volumes.

Olive stones are used  only  by some power plants as a fuel in combination with other biofuels. As an energy source olive stones are used  on much smaller range than olive cake. Price of olive stones is also much higher. Especially expensive can be “pale” olive stones with ash content below 2% (see the picture).

Olive stones could have limited use because of their hardness. Durability index (hardgrove index) of  olive cake for example is 20 (the harder the product, the lower durability index). Durability index of sunflower husks is 18 and of  olive  stones, which due to their  hardness are not  used in UK  as biomass, is  15. Of course durability would not be a problem for biomass dedicated power plants which have totally different construction of the mills. But coal mills are not strong enough for olive stones.

There are also some other industrial applications for  olive stones, for example in  production of  composite materials. Olive stones are also produced on olive oil second extraction factories, both in Spain and in Tunisia.